Your Brain on Fast Acting Carbs

What happens in the brain after eating too much refined carbohydrate? To answer this question, we gave twelve men with high BMI two milk shakes, one containing corn syrup (a highly processed and fast-acting carbohydrate) and the other with uncooked cornstarch (a slow-acting carbohydrate). Otherwise, the milk shakes had the same major nutrients (protein, fat, and carbohydrate) and similar sweetness, controlled by adding slightly different amounts of artificial sweetener. The milk shakes were given in random order, and neither the participants nor the study staff knew which came first.

The results were published in the American Journal of Clinical Nutrition. As we expected, blood glucose and insulin levels were higher after the fast-acting milkshake for the first hour or two. But by four hours after consuming the fast-acting shake, blood glucose fell to lower levels and reported hunger was greater, compared to the slow-acting shake. At that time, we conducted brain imaging scans, using a technique called functional magnetic resonance imaging (fMRI). The scans detected one brain region, called the nucleus accumbens that lit up like a laser after the fast-acting shake. The effect was so strong and consistent, it occurred in every one of our participants, providing strong statistical confidence in the results. The nucleus accumbens is considered ground zero for reward, craving, and addiction — including alcohol, tobacco, and cocaine abuse. Activation of this brain region on a weight loss diet would erode willpower, making sugary and starchy foods (which raise blood sugar most rapidly) exceedingly hard to resist.

The concept of food addiction is controversial because, unlike substances of abuse, we need food to live. However, this study suggests that highly processed carbohydrates may hijack basic reward circuitry in the brain, not because they are inherently so tasty (both milk shakes had the same sweetness), but instead because of direct actions on metabolism. Hunger is hard enough to fight under any circumstances, but once the nucleus accumbens joins in, it’s all over.

To get off the blood sugar roller-coaster ride and jump start weight loss, substitute those processed carbs for high quality fat, protein and natural carbohydrates.